Serum Amyloid P Component (SAP)

SAP can interact with DNA and histones and may scavenge nuclear material released from damaged circulating cells. May also function as a calcium-dependent lectin. It is a precursor of amyloid component P which is found in basement membrane and associated with amyloid deposits.

SAP is a member of the pentraxins family, characterised by calcium dependent ligand binding and distinctive flattened beta-jellyroll structure similar to that of the legume lectins. The name "pentraxin" is derived from the Greek word for five (penta) and berries (ragos) relating to the radial symmetry of five monomers forming a ring approximately 95 Aring across and 35 Aring deep. Human SAP has 51% sequence homology with C-reactive protein (CRP), a classical acute phase response plasma protein, and is a more distant relative to the "long" pentraxins such as PTX3 (a cytockine modulated molecule) and several neuronal pentraxins. Both SAP and CRP are evolutionary conserved in all vertebrates and also found in distant invertebrates such as the horseshoe crab (Limulus polyphemus).